Percutaneous interventional procedures to treat occlusive vascular disease, such as angioplasty, atherectomy and stenting, often dislodge material from the vessel walls. This dislodged material, known as emboli, enters the bloodstream, and may be large enough to occlude smaller downstream vessels, potentially blocking blood flow to tissue. If the blockage occurs in critical tissue, such as the heart, lungs, or brain, resulting ischemia poses a serious threat to the health or life of a patient.
Additionally, the deployment of stents and stent-grafts to treat aneurysms, ruptures, and other vascular diseases may result in the formation of clots or emboli. Such particulate matter also may cause infarction or stroke if released into the bloodstream. Furthermore, interventional procedures may generate foreign bodies that are left within a patient's bloodstream, thereby endangering the life of the patient. Foreign bodies may include, for example, a broken guide wire, pieces of a stent, or pieces of a catheter.
Numerous previously known methods and apparatus have been proposed to reduce complications associated with embolism, thrombus release, or foreign body material generation. U.S. Pat. No. 5,814,064 to Daniel et al. describes an emboli filter system having a radially expandable mesh filter disposed on the distal end of a guide wire. The filter is deployed distal to a region of stenosis, and any interventional devices, such as angioplasty balloons or stent delivery systems, are advanced along the guide wire. The filter is designed to capture emboli generated during treatment of the stenosis while permitting blood to flow through the filter. Similar filter systems are described in U.S. Pat. No. 4,723,549 to Wholey et al. and U.S. Pat. No. 5,827,324 to Cassell et al.
One disadvantage common to many prior art radially expandable filter systems, such as those described in the foregoing patents, is the number of parts necessary to fabricate the devices. Connecting more than a minimal number of such parts to a guide wire generally increases delivery complications. The ability of the guide wire to negotiate tortuous anatomy is reduced, and the profile of the device in its delivery configuration increases. Consequently, it may be difficult or impossible to use such devices in small diameter vessels, such as are commonly found in the carotid and coronary arteries, as well as in cerebral vasculature. Moreover, such filter devices are often incapable of preventing material from escaping from the filter during the process of collapsing the filter for removal.
Thus, there has been a long-felt need in the art for a simple, safe, and effective emboli filter that does not significantly impede antegrade blood flow, that reduces stress applied to the vessel wall, that conforms to the size and internal profile of the vessel in vivo to reduce escape of emboli past the filter, that may be collapsed for retrieval without loss of captured emboli, that may be sized for use in small vasculature, and that may be used in tortuous anatomy without increased delivery complications.
Foams are used in a variety of vascular medical applications. For example, U.S. Pat. No. 5,725,568 to Hastings describes the use of biocompatible foam as an occlusive agent during aneurysm repair. U.S. Pat. No. 5,837,140 to Fini et al. describes a blood filter fabricated from polyurethane foam. The filter is contained within a semirigid housing and is configured for use as part of an extracorporeal blood circuit. It is not suited for intravascular use.
U.S. Pat. Nos. 5,192,290 and 5,411,509 to Hilal, as well as U.S. Pat. No. 5,827,304 to Hart, describe embolectomy catheters having a portion comprising an expandable elastomeric foam that may be used to remove blood clots from a patient's vessel. These foam portions are substantially spherical and presumably occlude or impede antegrade flow through the vessel; they are therefore not suited for use as emboli filters.
U.S. Pat. No. 6,152,947 to Ambrisco et al. describes an embolic filter having a plastic or metal frame attached to a filter mesh. Foam seals may be attached to the frame so that the frame conforms to and sealingly engages the patient's vasculature. While foam seals may reduce emboli leakage around an embolic filter and may be less traumatic to vascular intima, as compared to other previously known filters, foam seals are an additional component that is expected to increase delivery profile and increase delivery complications. That patent states at column 3, lines 15-16, that the filter frame itself “may be metal, plastic, gel or foam or any combination thereof,” but provides no teaching as to how a filter frame fabricated exclusively from foam could be made or would function. Furthermore, Ambrisco does not describe a filter mesh fabricated from foam.
U.S. Pat. No. 6,010,531 to Donlon et al. describes a catcher adapted for placement in a patient's left ventricle during aortic valve replacement surgery to catch any debris released during leaflet removal, or in the debridement process. The catcher comprises a flexible, porous mesh, foam, gauze, or screen constructed as a bag or pouch with an opening on the top end. A flexible and resilient metal or elastomeric ring may be mounted to the catcher around the opening to allow the ring to collapse for delivery and to expand to engage the ventricular wall. The catcher is attached to a tether, such as a suture, to facilitate positioning within the ventricle.
Donlon's catcher device has several drawbacks that make it unsuitable for use as a vascular filter. The catcher is not disposed about a guide wire. It is not sized for use in small vasculature, and the metal or elastomeric ring mounted to the catcher would presumably kink if sized for such use. Furthermore, the metal ring would apply a potentially traumatic stress against the vessel wall.
U.S. Pat. No. 5,941,869 to Patterson et al. describes an embolic filter having a plurality of structural members that enclose and support a nonthrombogenic expandable filter medium. The structural members are made of metal or a polymer, and the expandable filter medium may be a porous foam material. As with previous filter devices, it is expected that the substantially rigid structural members will apply a stress to the vessel wall that may damage or traumatize the wall.
U.S. Pat. No. 6,165,200 to Tsugita et al. describes a filter assembly having a plurality of substantially cylindrical, expandable sponge-like elements that are adapted to engage the wall of a patient's vessel. The sponge-like elements are affixed to a guide wire and have sufficient porosity to allow blood, but not large emboli, to pass freely therethrough. Additionally, the sponge-like elements may have varying porosity that decreases along the length of the guide wire, so that embolic material enters a proximal portion of the elements, but is captured within a distal portion of the elements. The patent claims that varying porosity along the length of the guide wire substantially decreases a likelihood that embolic material will be caught only on an outer surface of the sponge-like elements, thus reducing the risk that emboli will be released when the sponge-like elements are retrieved within a sheath.
While it is expected that the filter assembly of the Tsugita patent will sealingly conform to the patient's vessel with reduced trauma or injury, the assembly has several drawbacks. Applicants disagree with the assertion in the Tsugita patent that varying porosity will substantially reduce the risk of emboli being liberated during retrieval. Red blood cells have an approximate diameter of 5 microns. Dangerous emboli, meanwhile, are commonly defined as particles greater than about 60-100 microns in diameter. Dangerous emboli, however, can vary in size as much as an order of magnitude. Thus, unless a very substantial variance in porosity is provided (a variance not feasible for sponge-like elements suitable used in small vasculature), it is expected that the largest and potentially most dangerous emboli may not, or may only partially, enter within the pores rather than be caught against an outer surface of the sponge-like elements. During retrieval, some or a portion or all of these larger particles may escape into the blood stream.
Providing a plurality of sponge-like devices as in the Tsugita patent is expected to have a number of drawbacks. First, a longer length of vessel is required to deploy the multiple sponge-like elements. Second, an increased risk of complications, e.g. snagging or frictional sticking, exists while collapsing the long length of sponge-like elements back to the delivery configuration. Third, the plurality of sponge-like elements reduces trackability through tortuous anatomy. Fourth, the length of the sponge-like elements, coupled with their density, is expected to reduce the pressure of blood passing through the elements, thus potentially causing ischemia or damage to downstream tissue. The density and length of the sponge-like elements also may require a volume of material to fabricate the cylinders that renders disposal of the elements within a delivery sheath having a delivery profile suited for small vasculature, for example, a delivery profile as small as 3 Fr, unfeasible.
An additional drawback of the sponge-like elements is that, even if dangerous emboli are captured within the pores, the emboli may be squeezed out of the pores during collapse of the elements back to the delivery configuration. This risk is especially acute due to the deployed, cylindrical profile of the sponge-like elements. The profile provides a sharp step, or discontinuity, to a retrieval sheath that is expected to increase retrieval complications.
In view of the foregoing disadvantages of previously known apparatus and methods, it would be desirable to provide a vascular filter that overcomes such disadvantages and employs few components.
It would be desirable to provide a vascular filter that conforms, and reduces a risk of trauma, to the vessel wall.
It also would be desirable to provide a vascular filter that is capable of being contracted to a small delivery profile, thus permitting use of the filter in small vessels.
It still further would be desirable to provide a vascular filter that reduces a risk of emboli or thrombus removed from the vessel wall escaping from the filter when the filter is collapsed and removed.
It would be desirable to provide a vascular filter that does not significantly impede antegrade blood flow.
It would be desirable to provide a vascular filter having a filter element fabricated solely from foam.